1. Field of the Invention
The present invention relates to a method for imprinting wafer-identifying information, and an exposure method and apparatus for imprinting wafer-identifying information, on wafers on which a plurality of thin-film devices are formed in a batch.
2. Description of the Related Art
Thin-film devices produced by thin-film fabrication technology include semiconductor devices and thin-film magnetic heads and the like. To produce such thin-film devices, a plurality of thin-film devices are formed in a batch on a wafer (substrate) using the thin-film fabrication technology or the like and thereafter this wafer is separated into individual thin-film devices.
Generally, for example, in order to control the fabrication process and to prevent the occurrence of defective devices, each of the aforementioned thin-film devices are provided with wafer-identifying information for identifying a wafer to which the thin-film device belongs and device location information for identifying the position of the thin-film device in the wafer. These pieces of information are imprinted on each wafer before the wafer is separated into individual thin-film devices. However, the step of imprinting the information may be performed before, during, or after the formation of the thin-film devices.
Conventionally, the following two methods have been typically adopted as methods for imprinting wafer-identifying information and device location information on wafers. The following explanations will be given assuming that a wafer is imprinted with, as wafer-identifying information, a wafer identification number that is different from one wafer to another, and, as device location information, a device location number that indicates a position of the thin-film device in a wafer.
According to the first method, device location numbers are imprinted using photolithography and wafer identification numbers are imprinted by laser marking. The first method is explained below with reference to the flowchart of FIG. 11. According to the first method, initially, a predetermined base is coated with a resist to form a resist layer (step S201). Then, using a mask having a pattern of a device location number drawn thereon, this resist layer is exposed in a batch to light for forming a latent image of the device location number (step S202). After the exposure, the resist layer is developed to form a patterned resist layer (step S203). Thereafter, the patterned resist layer may be entirely left unremoved so as to express the device location number with this patterned resist layer. Alternatively, using the patterned resist layer as a mask, the base of the patterned resist layer may be etched by ion milling or the like to imprint the device location number thereon. Then, a wafer identification number is entered to a laser marking apparatus (step S204). Subsequently, using the laser marking apparatus, the wafer identification number is imprinted by means of a laser beam, that is, laser marking is performed (step S205).
The second method employs laser marking to imprint wafer identification numbers and device location numbers. Now, the second method will be explained below with reference to the flowchart of FIG. 12. According to the second method, a wafer identification number is entered to a laser marking apparatus (step S211). Then, using the laser marking apparatus, a wafer identification number and a device location number are imprinted by means of a laser beam, that is, laser marking is performed (step S212). The device location number is generated in the laser marking apparatus by means of software, for example, so as to correspond to the thin-film device to be imprinted therewith.
The aforementioned first and second methods are described, for example, in Published Unexamined Japanese Patent Application (KOKAI) No. Hei 9-50606.
FIG. 13 is an explanatory view illustrating an exemplary configuration of the laser marking apparatus employed in the aforementioned first and second methods. The laser marking apparatus has an X-Y stage 302, on which a wafer 301 is to be placed, capable of moving in X and Y directions that are orthogonal to each other. The apparatus further has an X-direction position controller 303 for controlling the position of the X-Y stage 302 in the X direction, and a Y-direction position controller 304 for controlling the position of the X-Y stage 302 in the Y direction. The laser marking apparatus further has a laser beam source 305 for emitting a laser beam, a lens 306 for condensing the laser beam emitted from the laser beam source 305, and a mirror 307 for reflecting the laser beam condensed by the lens 306 to irradiate the wafer 301 on the X-Y stage 302 with the reflected laser beam. The laser marking apparatus further has a controller 308 for controlling the X-direction position controller 303, the Y-direction position controller 304, and the laser beam source 305, and has a storage device 309 connected to the controller 308. The storage device 309 stores the position in the wafer 301 to imprint information thereon, and the information to be imprinted on the wafer 301, and provides the controller 308 with these pieces of information as appropriate.
In accordance with the information stored in the storage device 309, the controller 308 of the laser marking apparatus shown in FIG. 13 allows the wafer 301 to be irradiated with the laser beam emitted from the laser beam source 305 while controlling the X-direction position controller 303 and the Y-direction position controller 304 to vary the position of the X-Y stage 302 and the wafer 301 placed thereon. This makes it possible to imprint the wafer identification number and the device location number at the predetermined position on each thin-film device in the wafer 301. Instead of varying the position of the X-Y stage 302 and the wafer 301, the laser beam may be moved by moving mirror 307, for example.
In both the first and second methods, at least wafer identification numbers are imprinted by laser marking, on the thin-film devices of a wafer one by one. Accordingly, there is a problem that much time is required for imprinting the information including the wafer identification number, and the time required for imprinting the information would increase as the number of thin-film devices on a wafer increases. In particular, in the case where the thin-film device is a thin-film magnetic head, the size of a wafer tends to increase while the thin-film device decreases in size. For this reason, it is conceivable that the number of thin-film devices in a wafer will become greater in the future and the time required for imprinting information such as wafer identification numbers per wafer will increase accordingly.
For example, suppose that information such as wafer identification number is imprinted by laser marking and that 0.5 seconds are required for imprinting on each thin-film device. In this case, for a 3-inch (76.2 mm) wafer having 4,000 thin-film devices formed thereon, 2,000 seconds (about 33 minutes) would be required for imprinting on each wafer. For a 6-inch (152.4 mm) wafer having 16,000 thin-film devices formed thereon, 8,000 seconds (about 2 hours and 13 minutes) would be required for imprinting on each wafer.
Device location numbers are not different among wafers having the same type of thin-film devices formed thereon. Accordingly, for such wafers, it is possible to imprint device location numbers through photolithography using a common mask on which the device location number is drawn, as in the first method. In the first method, the device location number is imprinted through photolithography, which saves the time required for laser marking. However, it requires an additional step of performing photolithography to imprint the device location number.
Published Unexamined Japanese Patent Application (KOKAI) No. Sho 62-20116 discloses a technique for imprinting device location numbers in a batch on all the devices in a thin-film magnetic head substrate, using photolithography. However, no description is found in this publication about imprinting wafer identification numbers.
Published Unexamined Japanese Patent Application (KOKAI) No. Hei 4-102214 discloses a technique for imprinting device location numbers and wafer identification numbers in a batch on a thin-film magnetic head substrate, using photolithography. However, this technique presents a problem that it requires masks for exposure as many as the number of varieties of the wafer identification numbers, thereby raising the manufacturing cost of the devices.
Published Unexamined Japanese Patent Application (KOKAI) No. Hei 4-356717 discloses a technique for imprinting a group of symbols on a thin-film magnetic head substrate using a photomask for forming a plurality of symbols and a photomask for erasing any of the plurality of symbols. This technique expresses information by the combination of the presence and absence of a plurality of symbols, and therefore there is a problem that the varieties of expressible information is smaller in number, for the number of symbols. On the other hand, the aforementioned Published Unexamined Japanese Patent Application (KOKAI) No. Hei 4-356717 describes that only two photomasks are required. However, the technique disclosed in this publication requires the erasing photomasks as many as the number that is obtained by subtracting 1 from the number of varieties of expressible information. Therefore, it also presents the problem of raising the manufacturing cost of the devices.
It is therefore an object of the present invention to provide a method for imprinting wafer-identifying information and an exposure method and apparatus for imprinting wafer-identifying information, capable of imprinting wafer-identifying information on wafers on which a plurality of thin-film devices are formed in a batch, in a short time and without requiring a number of exposure masks.
The present invention provides a method for imprinting wafer-identifying information on wafers each having a plurality of thin-film devices formed thereon in a batch, using a patterned resist layer. The wafer-identifying information includes a plurality of digits, each digit being expressed with a numeral or a symbol. The method comprises the steps of: selecting a wafer to be imprinted with the wafer-identifying information; forming a resist layer on the selected wafer; exposing the resist layer, using a mask, to light for forming a latent image of the wafer-identifying information; and forming the patterned resist layer by developing the exposed resist layer. In the step of exposing the resist layer, a mask on which a pattern of a numeral or the symbol to be imprinted is drawn thereon is selected for each digit of the wafer-identifying information in which the numeral or the symbol is changeable wafer by wafer.
According to the method for imprinting wafer-identifying information of the present invention, a mask on which a pattern of a numeral or the symbol to be imprinted is drawn thereon is selected for each digit of the wafer-identifying information in which the numeral or the symbol is changeable wafer by wafer, and exposure is performed using the selected mask.
In the method for imprinting wafer-identifying information of the present invention, in the step of exposing the resist layer, the selection of a mask on which the pattern of a numeral or the symbol to be imprinted is drawn thereon and the exposure using the selected mask may be repeated as many times as the number of digits of the wafer-identifying information, so that exposure is performed for all digits of the wafer-identifying information.
In the method for imprinting wafer-identifying information of the present invention, in the step of exposing the resist layer, the resist layer may be further exposed to light for forming a latent image of device location information for identifying a position of a thin-film device in the wafer, using a mask on which a pattern of the device location information is drawn thereon.
Furthermore, in the method for imprinting wafer-identifying information of the present invention, the numeral or symbol of each digit of the wafer-identifying information may vary in accordance with a certain rule in response to change of one selected wafer to another, and, in the step of exposing the resist layer, one selected mask may be changed to another in response to the change of one selected wafer to another in such a manner as to correspond to the rule of the variation of the numeral or symbol of each digit of the wafer-identifying information.
Furthermore, in the method for imprinting wafer-identifying information of the present invention, in step of exposing the resist layer, a positional relationship between the mask and the wafer may be changed for each digit of the wafer-identifying information, so that the numeral or symbol of each digit of the wafer-identifying information is imprinted at a mutually different position.
Furthermore, the method for imprinting wafer-identifying information of the present invention may further comprise the step of etching a layer underlying the patterned resist layer, using the patterned resist layer as an etching mask.
Furthermore, the method for imprinting wafer-identifying information of the present invention may further comprise the step of forming a plating layer by performing plating with the patterned resist layer used as a frame.
The present invention also provides an exposure method for imprinting wafer-identifying information. The exposure method is used for imprinting wafer-identifying information on wafers each having a plurality of thin-film devices formed thereon in a batch, using a patterned resist layer, the wafer-identifying information including a plurality of digits, each digit being expressed with a numeral or a symbol. The exposure method exposes the patterned resist layer formed on the wafer to light for forming a latent image of the wafer-identifying information, and comprises the steps of: selecting a wafer to be imprinted with the wafer-identifying information, and exposing the resist layer of the selected wafer, using a mask, to the light for forming the latent image of the wafer-identifying information. In the step of exposing the resist layer, exposure is performed for each digit of the wafer-identifying information in which the numeral or the symbol is changeable wafer by wafer, by selecting a mask on which a pattern of a numeral or the symbol to be imprinted is drawn thereon for each digit.
In the exposure method for imprinting wafer-identifying information according to the present invention, a mask on which a pattern of a numeral or the symbol to be imprinted is drawn thereon is selected for each digit of the wafer-identifying information in which the numeral or the symbol is changeable wafer by wafer, and exposure is performed using the selected mask.
In the exposure method for imprinting wafer-identifying information according to the present invention, in the step of exposing the resist layer, the selection of a mask on which the pattern of a numeral or the symbol to be imprinted is drawn thereon and the exposure using the selected mask may be repeated as many times as the number of digits of the wafer-identifying information, so that exposure is performed for all digits of the wafer-identifying information.
Furthermore, in the exposure method for imprinting wafer-identifying information according to the present invention, in the step of exposing the resist layer, the resist layer may be further exposed to light for forming a latent image of device location information for identifying a position of a thin-film device in the wafer, using a mask on which a pattern of the device location information is drawn thereon.
Furthermore, in the exposure method for imprinting wafer-identifying information according to the present invention, the numeral or symbol of each digit of the wafer-identifying information may vary in accordance with a certain rule in response to change of one selected wafer to another, and, in the step of exposing the resist layer, one selected mask may be changed to another in response to the change of one selected wafer to another in such a manner as to correspond to the rule of the variation of the numeral or symbol of each digit of the wafer-identifying information.
Furthermore, in the exposure method for imprinting wafer-identifying information according to the present invention, in step of exposing the resist layer, a positional relationship between the mask and the wafer may be changed for each digit of the wafer-identifying information, so that the numeral or symbol of each digit of the wafer-identifying information is imprinted at a mutually different position.
The present invention also provides an exposure apparatus for imprinting wafer-identifying information. The exposure apparatus is used for imprinting wafer-identifying information using a patterned resist layer on wafers each having a plurality of thin-film devices formed thereon in a batch, the wafer-identifying information including a plurality of digits, each digit being expressed with a numeral or a symbol. The exposure apparatus exposes the patterned resist layer formed on the wafer to light for forming a latent image of the wafer-identifying information, and comprises: a wafer selecting device for selecting a wafer to be imprinted with the wafer-identifying information, and an exposure device for exposing the resist layer of the wafer selected by the wafer selecting device, using a mask, to the light for forming the latent image of the wafer-identifying information. The exposure device has a mask selecting device for selecting a mask on which a pattern of a numeral or symbol to be imprinted is drawn thereon for each digit of the wafer-identifying information in which the numeral or the symbol is changeable wafer by wafer.
According to the exposure apparatus for imprinting wafer-identifying information of the present invention, a mask on which a pattern of a numeral or the symbol to be imprinted is drawn thereon is selected for each digit of the wafer-identifying information in which the numeral or the symbol is changeable wafer by wafer, and exposure is performed using the selected mask.
In the exposure apparatus for imprinting wafer-identifying information according to the present invention, the exposure device may repeat the selection of a mask on which the pattern of a numeral or the symbol to be imprinted is drawn thereon and the exposure using the selected mask as many times as the number of digits of the wafer-identifying information, so as to perform exposure for all digits of the wafer-identifying information.
Furthermore, in the exposure apparatus for imprinting wafer-identifying information according to the present invention, the exposure device may further expose the resist layer to light for forming a latent image of device location information for identifying a position of a thin-film device in the wafer, using a mask on which a pattern of the device location information is drawn thereon.
Furthermore, in the exposure apparatus for imprinting wafer-identifying information according to the present invention, the numeral or symbol of each digit of the wafer-identifying information may vary in accordance with a certain rule in response to change of one selected wafer to another, and, the mask selecting device may change one selected mask to another in response to the change of one selected wafer to another in such a manner as to correspond to the rule of the variation of the numeral or symbol of each digit of the wafer-identifying information.
Furthermore, in the exposure apparatus for imprinting wafer-identifying information according to the present invention, the exposure device may further have a position changing device for changing a positional relationship between the mask and the wafer for each digit of the wafer-identifying information, so that the numeral or symbol of each digit of the wafer-identifying information is imprinted at a mutually different position.
Other objects, features, and advantages of the present invention will be apparent from the following description.